1. Field of the Invention
The present invention relates to a lens device for moving lenses in an optical-axis direction, an imaging device using the lens device, and a cell-phone with a camera using the lens device.
2. Description of the Related Art
In a conventionally known electronic camera, a zoom lens barrel is adapted to protrude in two or three steps for the purpose of downsizing the camera. When the camera is not used, the zoom lens barrel is collapsed to minimize the size in an optical-axis direction. Meanwhile, an imaging device built in a small-sized equipment of a cell-phone and so forth is extremely small in comparison with a normal electronic camera. Thus, components of such an imaging device, which are a lens, a CCD (Charge Coupled Device) and so forth, are considerably restricted regarding its size. Moreover, a space for containing the components is considerably restricted as well. For this reason, this kind of the small-sized equipment has an insufficient shooting function and insufficient image quality on a taken image when used as an alternative equipment of the electronic camera. In general, this kind of the small-sized equipment is restrictedly used for a case of shooting in that image quality is not particularly required. For example, this kind of the small-sized equipment is used for a case in that an image is taken as a substitution of a note, and for a case in that an image for standby display of a cell-phone is taken.
With respect to the above, in resent years, a downsized high-pixel CCD and a downsized lens have been developed so that quality of an image, which is taken by using the small-sized equipment of the cell-phone, a PDA and so forth, is rapidly improved. The remaining problem is to enhance the shooting function, and it is especially desired to provide an automatic-focus function and a zoom function, which are usually provided to the normal electronic camera, to the small-sized equipment. Some of the recent camera-equipped cell-phones have both of the 2× optical zoom function and the automatic-focus function (Trade Name: Vodafone V602SH).
The automatic-focus function and the zoom function are carried out by moving lenses inside the imaging device in an optical-axis direction. As to the electronic cameras and electronic video cameras, some lens-driving methods are known. In one of the lens-driving methods, rotation of a DC motor and a stepping motor is utilized, and in another thereof, contracting and expanding of a piezoelectric device are utilized. When adopting these methods to the small-sized equipment of the cell-phone and so forth, it is considered that a method employing a hollow stepping motor is preferable in view of miniaturization of the device and accuracy for controlling the movement of the lens. In this method employing the hollow stepping motor, the lens is moved by supplying a pulse current to a stator surrounding a cylindrical hollow rotor, which surrounds a lens barrel holding the lens. As the lens-driving method utilizing the hollow stepping motor, is proposed for example a method in which a lens group is moved inside a lens unit (fixed barrel) in an optical-axis direction (see Japanese Patent Laid-Open Publication No. 56-147132, for instance).
However, when the zoom function and the automatic-focus function are provided to the camera used for the small-sized equipment, a number of parts increases. Consequently, there arise problems in that assembling a camera unit becomes difficult and production cost increases. Moreover, there arises another problem in that it is difficult to prevent positions of the lens groups from shifting and to accurately adjust optical axes of the lens groups.